Abstract ? Infectious Disease Epidemiology and Theory Core The overarching goal of the Infectious Disease Epidemiology and Theory Core (IDET) is to support and train CDUHR investigators to apply theories and knowledge about multilevel factors that influence HIV transmission, natural history, prevention and clinical care to the development of high-impact research that will contribute to Ending HIV/AIDS among people who use drugs (PWUD). The IDET Core has the following Specific Aims: 1) Support CDUHR investigators in applying and integrating knowledge and theory about substance use and HIV to their research; 2) Provide training on multilevel factors that may promote or impede progress toward Ending HIV/AIDS; and 3) Develop and disseminate new transdisciplinary frameworks and theories to guide the study of HIV among PWUD. Core members are expert in the study, prevention, care and treatment of HIV infection and its co- morbidities, and all have been with the Center for many years. The Core will provide training and consultation, and will take the lead within the Center on bringing emerging scientifically relevant issues, new theories, and advances in biomedical and clinical aspects of HIV and substance use to CDUHR investigators. The IDET Core will collaborate with other Cores and Center Leadership to support CDUHR investigators to acquire new knowledge related to the complex problem of HIV among PWUD.